Heretofore, it has been known to provide frost warnings for pipes by mechanical means which relied upon expansion of water in an auxiliary narrow diameter pipe to protect a larger diameter pipe. Such a device is shown in U.S. Pat. No. 1,446,783 Calinaud issued Feb. 27, 1923. Not only is such a device expensive to install but also it is relatively unreliable and can result in burst pipes before remedial action can be taken.